1. Field of the Invention
The present invention relates to an optical cable, for example an optical cable which can be used in a work place such as an office building to connect a plurality of devices which receive and/or transmit data. The invention further relates to a method of laying the optical cable, and a data transfer system using the optical cable.
2. Description of the Prior Art
It is known to transmit data to, from or between devices (appliances) in a room such as an office using a data transfer system which employs electric cables laid under the flooring. Such a system can be easily modified to cope with an alteration of office layout, such as movement of devices or an increase in the number of devices.
In the above system, a wiring channel which is approximately U-shaped in section is provided under the flooring. The wiring channel is in the shape of a matrix or grid, and has lower and side surfaces which extend perpendicularly to each other. Electric cables (each containing a plurality of copper electric wires) for transmission of signals are laid along the wiring channel and run out of the wiring channel into the room at positions corresponding to locations where devices are installed.
Because of the increase in multiplex communication in recent years, there is a growing demand for an "optical composite" data transfer system which uses both electric cables and optical cables for transmission of signals. In such a system, one or more optical cables for optical communication are laid in the wiring channel alongside the electric wire cables.
FIG. 14 is a sectional view showing an optical cable 100 having a conventional construction. The optical cable 100 includes four optical fibers 102 twisted together around a reinforcing tension member 101. A tape 103 is wound around the optical fibers 102, and a plastics covering layer 104 provided for protection around the tape 103. The tape 103 and the plastics covering layer 104 protect the optical fibers 102 from being subjected to external force.
However, the optical cable 100 as described above has a low degree of flexibility. Thus, the minimum permissible radius of curvature of the optical cable 100 may be as large as 100-120 mm. Thus, there are cases in which the optical cable 100 cannot be laid within a wiring channel formed in the shape of a matrix.
The optical cable 100 shown in FIG. 14 has another problem because of its large diameter. For example, the optical cable 100 may be too wide to be inserted into a wiring channel which already accommodates an electric wire.